[PATCH] tree-optimization/114203 - wrong CLZ niter computation

[Richard Biener]

For precision less than int we apply the adjustment to make it defined
at zero after the adjustment to make it compute CLZ rather than CTZ.
That's wrong.

Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed.

        PR tree-optimization/114203
        * tree-ssa-loop-niter.cc (build_cltz_expr): Apply CTZ->CLZ
        adjustment before making the result defined at zero.

        * gcc.dg/torture/pr114203.c: New testcase.
---
 gcc/testsuite/gcc.dg/torture/pr114203.c | 21 +++++++++++++++++++++
 gcc/tree-ssa-loop-niter.cc              |  7 +++----
 2 files changed, 24 insertions(+), 4 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/torture/pr114203.c

diff --git a/gcc/testsuite/gcc.dg/torture/pr114203.c 
b/gcc/testsuite/gcc.dg/torture/pr114203.c
new file mode 100644
index 00000000000..0ef6279942a
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr114203.c
@@ -0,0 +1,21 @@
+/* { dg-do run } */
+
+int __attribute__((noipa))
+foo (unsigned char b)
+{
+  int c = 0;
+
+  while (b) {
+      b >>= 1;
+      c++;
+  }
+
+  return c;
+}
+
+int main()
+{
+  if (foo(0) != 0)
+    __builtin_abort ();
+  return 0;
+}
diff --git a/gcc/tree-ssa-loop-niter.cc b/gcc/tree-ssa-loop-niter.cc
index 038e4331661..c6d010f6d89 100644
--- a/gcc/tree-ssa-loop-niter.cc
+++ b/gcc/tree-ssa-loop-niter.cc
@@ -2288,6 +2288,9 @@ build_cltz_expr (tree src, bool leading, bool 
define_at_zero)
        src = fold_convert (unsigned_type_node, src);
 
       call = build_call_expr (fn, 1, src);
+      if (leading && prec < i_prec)
+       call = fold_build2 (MINUS_EXPR, integer_type_node, call,
+                           build_int_cst (integer_type_node, i_prec - prec));
       if (define_at_zero)
        {
          tree is_zero = fold_build2 (NE_EXPR, boolean_type_node, src,
@@ -2295,10 +2298,6 @@ build_cltz_expr (tree src, bool leading, bool 
define_at_zero)
          call = fold_build3 (COND_EXPR, integer_type_node, is_zero, call,
                              build_int_cst (integer_type_node, prec));
        }
-
-      if (leading && prec < i_prec)
-       call = fold_build2 (MINUS_EXPR, integer_type_node, call,
-                           build_int_cst (integer_type_node, i_prec - prec));
     }
 
   return call;
-- 
2.35.3